The present invention is directed to a method for generating measuring signals for measuring the transmission properties of handsfree telecommunications devices. Handsfree equipment in telephones are electrical message systems comprising specific transmission links for voice transmission wherein the transmission links are mutually influenced by crosstalk. The possibility of being able to xe2x80x9ctalk handsfreexe2x80x9d with a telephone significantly enhances the operating comfort of a telephone and the quality of a telephone call. Handsfree devices enable call situations like those that occur in natural conversation between talking parties and allow a significantly greater freedom of movement and action of the person speaking handsfree. Voice-controlled signal processing mechanisms are utilized in order, on the one hand, to get control of the discussion and listening-in conditions that clearly deteriorate compared to ordinary handset-bound telecommunication and, on the other hand, to minimize the risk of occurring feedback. As is known, the voice-controlled signal processing in handsfree telephones ensues by
1) voice-dependently switched attenuations in the respective transmission and reception paths (attenuation control of the transmission and reception paths; principle of the level scale),
2) dynamic compression methods,
3) frequency-selective level scales,
4) decorrelation of the transmission and reception signals, and
5) adaptive compensation of acoustic echos.
Over and above this, the phenomenon of double talk is a critical feature of handsfree devices. The remote subscribers communicating with one another can thereby talk simultaneously. Of the aforementioned methods employed in handsfree devices for signal processing, adaptive compensation of acoustic echos (constructing adaptive echo compensators) in handsfree devices especially leads to a considerably reduced attenuation boost of the respectively employed level scale. Double talk only becomes possible as a result thereof because, transmission and reception paths are simultaneously active on principle. However, the utilization of echo compensators does not yet assure an unproblematical double talk mode because the adaption algorithms that are employed react more or less sensitively to changes in the room (place at which the handsfree telephone is put) and disturbances due to double talk phases. Moreover, the finite adaption speed may result in a disturbing increase or too slow a decrease of the echos under certain circumstances. It is precisely the double talk occurring in handsfree devices that is greatly deteriorated by the aforementioned signal processing mechanisms. So that true-to-life conversations (acquisition of the real double talk call situation) can be realized with the handsfree devices, the auditively relevant parameters must, on the one hand, be extracted, and the instrumentally measurable, technical parameters that describe the handsfree device must be acquired. Instrumentally measurable parameters for characterizing the conversation parameters of a handsfree device are not contained in measurement rules currently under discussionxe2x80x94such as, for example, the publication prI-ETS 300-245-3, Part 3; PCM A-Law, Loudspeaking and Handsfree Telephony, Stockholm, November 1994 (approval regulation). No measurements whatsoever are specified either for the double talk parameters or for the attenuation control of the two transmission paths (transmission and reception paths). In order to nonetheless be able to make statements at all with respect to the conversation parameters of handsfree devices, it is at least necessary that, first, the attenuation boost realized in a handsfree device designed in conformity with the indicated approval regulation and, second, the attenuation distribution on the two transmission paths of the handsfree device in the quiescent condition are known. Neither statements that characterize the behavior of the handsfree device during a double talk event nor farther-reaching analyses of the transmission quality during the double talk event are possible with these two parameters because other technical parameters such as, for example, the prioritization of voice direction, switching times, blocking times, etc., play a part therein. In order to acquire the behavior of voice-controlled devices quite generally dependent on the time and level conditions of the two input signals, the publication Fortschritte der Akustikxe2x80x94DAGA 1993, Bad Honnef, DPG GmbH, pages 932-935; F. Kettler, xe2x80x9cNeue Messmethodik zur Bestimmung der xc3x9cbertragungseigenschaften von Sprachechokompensatoren in Fernsprechnetz fxc3xcr Enzelmessungen und Tandemschaltungenxe2x80x9d discloses that two xe2x80x9ccomposite sourcexe2x80x9d signals with different cycle durations be employed. A suitable simulation and analysis of a time segment is thereby possible, whereby the two signals are simultaneously fed in (true double talk). Whether one voice path is prioritized, whether both voice paths are attenuated in alternation or, for example, whether a fixed attenuation distribution of both paths during double talk is present can be determined from the transmitted sequence.
FIG. 1 shows a measuring arrangement MA constructed according to ITU (International Telecommunication Union) publication Volume Vxe2x80x94RECOMMENDATION P.34, Melbourne, 1988, pages 64 through 71, particularly Ch. 6, for measuring the transmission properties of a handsfree device FSE or a handsfree telephone FST in the xe2x80x9cdouble talkxe2x80x9d call situation. To this end, the handsfree device FSE is connected to a handsfree loudspeaker FL in a transmission direction (transmission path) via a first amplifier V1. In a reception direction (reception path), a handsfree microphone FM is connected to the handsfree device FSE via a second amplifier V2. Given the illustrated measuring arrangement MA, the double talk call situation occurring during handsfree calling is achieved in that an xe2x80x9cartificial earxe2x80x9d KO and an xe2x80x9cartificial mouthxe2x80x9d KM are allocated to the handsfree loudspeaker FL and to the handsfree microphone FM, respectively, for simulating the handsfree conditions. The measuring arrangement MA also contains a measuring system MS in order to be able to acquire transmission properties of the handsfree device FSE. For simulating the real handsfree conditions, this measuring system MS supplies the handsfree device FSE with, first, a xe2x80x9cremotexe2x80x9d first transmission signal (measured signal) SS1 via a transmission/reception duplexer SEW preceding the handsfree device FSE that proceeds via the handsfree loudspeaker FL to the xe2x80x9cartificial earxe2x80x9d KO and, second, supplies it with a xe2x80x9cnearxe2x80x9d second transmission signal (measured signal) SS2 via the xe2x80x9cartificial mouthxe2x80x9d KM and the handsfree microphone FM. In the present case, the signals SS1, SS2 are preferably selected such that their properties correspond to those of a natural voice signal (for example, crest factor, envelope, spectral composition, etc.).
The measurement of the transmission properties of the handsfree device FSE is implemented in the measuring system MS. To that end, the signals SS1, SS2 sent from the measuring system MS are compared to a first reception signal ES1 received by the measuring system MS via the xe2x80x9cartificial earxe2x80x9d KO and to a second reception signal ES2 received by the measuring system MS via the transmission/reception duplexer SEW.
Analogous to the real handsfree conditions, the known crosstalk phenomenon occurs in the present measuring arrangement due to the infeed of the signals SS1, SS2. This crosstalk is expressed therein that a first crosstalk signal xc3x9cS1 related to the first transmission signal SS1 (for example, due to measuring arrangement and signal propagation properties) proceeds into the handsfree microphone FM in addition to the second transmission signal SS2, and that a second crosstalk signal xc3x9cS2 related to the second transmission signal SS2 (for example, due to measuring arrangement and signal propagation properties) proceeds into the xe2x80x9cartificial earxe2x80x9d KO in addition to the first transmission signal SS1. However, the measurement of the transmission properties of the handsfree device FSE is falsified by this crosstalk (undesired effect). Since crosstalk is fundamentally unavoidable in handsfree calling, efforts have therefore been made to acquire the influences of the crosstalk in order to be able to take the results resulting therefrom into consideration in the construction of the handsfree devices.
Given extremely simply constructed handsfree devices, wherein a frequency-independent level scale is employed, the measurement of the transmission properties of the handsfree device FSE can be undertaken with two mono-frequency signals differing in frequency.
When, however, telephones with modern handsfree devices (adaptive filter, dynamic characteristics matching, noise suppression, etc.) are to be measured, then the signals must have the properties of natural speech (for example, crest factor, envelope, spectral composition, etc.) both in the time domain as well as in the frequency domain.
An object of the present invention is to generate measuring signals for measuring systems for measuring the transmission properties of transmission links that mutually influence one another due to crosstalk, particularly of handsfree devices, such that the measurement of the transmission properties is not falsified by occurring crosstalk influences.
This object is achieved in accordance with the invention in a method of generating a plurality k of source signals s;
defining a (kxe2x88x92n+1)th source signal length xkxe2x88x92n+1 of a (kxe2x88x92n+1)th source signal Skxe2x88x92n+1 with xkxe2x88x92n+1 signal parts
a1kxe2x88x92n+1, a2kxe2x88x92n+1, a3kxe2x88x92n+1 . . . axkxe2x88x92n+1xe2x88x921, axkxe2x88x92n+1,
said source signal length x being x 0, and said coefficient n being n {2 . . . k};
defining a kth source signal length xk of a kth source signal sk with xk signal parts
a1k, a2k, a3k . . . axkxe2x88x921, axk;
calculating a measuring signal length m as m=nxe2x80x2mxe2x80x2, said n being nxe2x80x2 0 and said mxe2x80x2 being mxe2x80x2=2ent((ld(max{xkxe2x88x92n+1, xk}))+0.5;
lengthening said (kxe2x88x92n+1)th source signal skxe2x88x92n+1 to said measuring signal length m by attaching mxe2x88x92xkxe2x88x92n+1 zeros to an end of said (kxe2x88x92n+1)th source signal skxe2x88x92n+1;
lengthening said kth source signal sk to said measuring signal length m by attaching mxe2x88x92xk zeros to an end of said kth source signal sk; and
modifying said lengthened (kxe2x88x92n+1)th source signal skxe2x88x92n+1, and said lengthened kth source signal sk such that said (kxe2x88x92n+1)th source signal skxe2x88x92n+1 and said kth source signal sk being essentially orthogonal.
The idea underlying the invention is comprised therein that measuring signals (for example, the transmission signals SS1, SS2 of FIG. 1) that are essentially orthogonal are generated from respectively at least two voice or test signals (xe2x80x9ck=2xe2x80x9d source signals) in the time or frequency domain in the measuring system for measuring the transmission properties of transmission links that mutually influence one another due to crosstalk, particularly of handsfree devices. The remaining properties of the measuring signals are defined by the properties of the voice or test signals employed. Preservation of the properties is important in order to be able to investigate the dynamic behavior of transmission links that mutually influence one another due to crosstalk, particularly the handsfree devices, with real voice signals or specific test signals.
The orthogonality relationship is thereby not used in the mathematically exact sense, i.e. two vectors x, y of a Euclidean vector space V are orthogonal exactly when (x, y)=0 applies, but in a version de-intensified to finite precision: two vectors x, y of a Euclidean vector space V are orthogonal whenxe2x80x94analogous to claim 2xe2x80x94|x, y| less than  less than |x| |x, y| less than  less than |y| apply.
The object of the invention is also achieved in a device having a measuring system operating according to the method.